The present invention relates to the texturing of magnetic data storage media, and more particularly to the texturing of dedicated transducing head contact zones (also called landing zones) of such media to reduce transducing head flying heights while also minimizing stiction.
Laser treated magnetic disks, particularly those textured over areas designed for contact with data transducing heads, are known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules, rather than rims. In some cases, each of the domes is surrounded by a raised rim. The features can have either circular or elliptical profiles.
Collectively, the texturing features form a texture pattern or distribution throughout the head contact zone. A particularly preferred pattern is a spiral, formed by rotating the disk at a controlled angular speed while moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. The disk rotational speed and pulsing frequency together determine the circumferential pitch, i.e., the distance between adjacent texturing features in the spiral. Meanwhile, the radial speed of the laser controls the radial pitch or spacing between subsequent turns of the spiral. Frequently, the circumferential pitch and radial pitch are approximately the same, e.g., 20-30 microns. This spacing results in multiple texturing features cooperating to support a data transducing head at rest in the landing zone, given that the length and width dimensions of transducing head sliders typically are in the millimeter range.
The texturing features themselves can be made with a high degree of uniformity in size and shape, by maintaining a consistent laser power, focal spot size and pulse duration. As transducer glide heights (flying heights) continue to decrease, particularly below 1 microinch (25 nm), it becomes increasingly difficult for a texture to accommodate the glide height, and at the same time minimize stiction. The following table illustrates different measurements of three values, all in nm: an average height of multiple texturing features (Rp); the standard deviation of the height (.sigma.); and the measured glide avalanche. Glide avalanche occurs when a measured signal output exceeds a certain threshold, indicating that the transducing head is flying "too close" to the surface.
TABLE Rp .sigma. Glide Avalanche 15.2 1.4 18.8 15.5 1.2 18.2 18.0 1.6 18.8 18.7 1.1 21.1 19.7 1.8 24.6 19.8 1.6 25.8 23.0 1.5 30.5 23.6 1.5 27.0
From the table, it is seen that to avoid undue risk of collisions of the transducing head with the texturing features, while at the same time maintaining a flying height of about 25 nm, the average height of the features should be less than about 20 nm.
At the same time, the need to minimize friction and stiction imposes limits on the minimum heights of the texturing features. Typically, a liquid lubricant is applied to the surfaces of magnetic data storage disks, to improve wear characteristics and reduce dynamic friction. However, the liquid lubricant has the undesirable effect of contributing to stiction, the tendency of a data transducing head, once at rest against a magnetic disk, to adhere to the disk. This provides at least momentary resistance when the disk begins to rotate, potentially damaging both the disk and the transducing head, and risking loss of data.
A primary cause of stiction is the tendency of the liquid lubricant, through capillary action, to flow about and surround the texturing features in contact with an at-rest transducing head, even flowing to the head itself as indicated in FIG. 1, where h indicates the height of a data transducing head when at rest upon the texturing features, two of which are shown. The texturing features, nodules or bumps, are flattened slightly by the head over an area of contact with a radius r. By comparison, r.sub.m is the radius of the liquid lubricant meniscus surrounding each texturing feature, with each feature having a radius R at its base. The value d represents the thickness of the liquid lubricant film over surface areas away from the nodules. Thus, a meniscus of the liquid lubricant surrounds each texturing feature, occupying the full height between the transducing head and disk surface, clinging to the transducing head to provide momentary resistance to disk acceleration.
As seen in the chart of FIG. 2, the stiction effect increases dramatically as the height of texturing features decreases below 12 nm.
In view of the above, one option for achieving a I microinch glide height while minimizing stiction appears to be maintaining texturing feature heights within the range of 13-19 nm. However, given the lack of absolute precision in laser beam generation and optical components that focus and otherwise shape the laser beam, variance in substrate materials and parameters, and variance in the slider bodies that aerodynamically determine transducing head flying heights, the required degree of control is not practical. Further, when the heights of texturing features are reduced, their diameters are reduced as well, and it may be desirable to maintain larger diameter nodules or other features to enhance structural stability.
Therefore, it is an object of the present invention to provide a substrate for a data storage medium having a landing zone textured to accommodate glide heights less than 25 nm, while simultaneously minimizing stiction.
Another object is to provide a landing zone surface texture utilizing larger texturing features with greater heights, in combination with recessed regions surrounding the texturing features to accommodate liquid lubricant and thereby counteract the tendency of capillary flow toward a transducing head at rest on the landing zone.
A further object is to provide an improved process for texturing substrates and for fabricating magnetic data recording media to exhibit improved resistance to stiction despite lower transducing head flying heights.
Yet another object is to provide a data storage medium having improved wear characteristics and the tendency to afford increased longevity to data transducing heads used in conjunction with the medium.